The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications network wish to reduce the running costs of the base station. One option to do this is to implement a radio system as an antenna-embedded radio forming an active antenna array. Many of the components of the antenna-embedded radio may be implemented on one or more chips.
Nowadays active antenna arrays are used in the field of mobile communications systems in order to reduce power transmitted to a handset of a customer and thereby increase the efficiency of the base transceiver station, i.e. the radio station. The radio station typically comprises a plurality of antenna elements, i.e. an antenna array adapted for transceiving a payload signal. Typically the radio station comprises a plurality of transmit paths and receive paths. Each of the transmit paths and receive paths are terminated by one of the antenna elements. The plurality of the antenna elements used in the radio station typically allows steering of a beam transmitted by the antenna array. The steering of the beam includes but is not limited to at least one of: detection of direction of arrival (DOA), beam forming, down tilting and beam diversity. These techniques of beam steering are well known in the art.
The active antenna array or active antenna system is typically mounted on a mast or tower. The active antenna array is coupled to the base transceiver station (BTS) by means of a fibre optics cable and a power cable. The base transceiver station is coupled to a fixed line telecommunications network operated by one or more operators.
Equipment at the base of the mast as well as the active antenna array mounted on the mast is configured to transmit and receive radio signal within limits set by communication standards.
The code sharing and time division strategies as well as the beam steering rely on the radio station and the active antenna array to transmit and receive within limits set by communication standards. The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from the handset to the radio station as well as for a downlink communication from the radio station to the subscriber device.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications uses different frequencies in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use 900 MHz and 1800 MHz bands.
As technology evolves, the operators have expressed a desire for an active antenna product that is able to utilise the existing base-station investments, in addition to providing a new system/band. For example, in the roll-out of long term evolution (LTE) at 700 MHz (US) or 800 MHz (EU), the operators would like to deploy a single antenna at the masthead which could transmit the existing 900 MHz (EU) or 850 MHz (US) GSM signals, using equipment at the base of the mast, as well as providing active antenna functionality for the new LTE installation.
FIG. 1 shows an example of an active antenna system 10 as known in the prior art. The active antenna system 10 comprises a power supply unit 12, a central processing unit 20 plus a calibration feedback radio 25 and a plurality of transceiver units 50. In one aspect of the invention sixteen transceiver units 50 are present. It would be also possible to have four, eight or twenty transceiver units 50, but the number of transceiver units is not limiting of the invention.
Each one of the transceiver units 50 requires individual bi-directional high-speed digital data cables 22 to the central processing unit 20 as well as an individual analog RF coaxial line 23 to the calibration feedback radio 25. Furthermore, all of the transceiver units 50 require an individual select line (at lower speed digital) from the central processing unit 20. All of the transceiver units 50 have at least two shared power supply lines from the power supply unit 12. Currently data cables 22 in the form of jumper leads make the connection between the central processing unit 20 and the individual transceiver unit 50. These data cables 22 have a known length, but experience shows that these known lengths can slightly vary from an active antenna system 10 to active antenna system 10. This slight variation in length of the data cables 22 between the central processing unit 20 and the transceiver units 50 due to the slight variation of length in the data cables 22 means that the phases of the signals are slightly different in each of the active antenna systems 10. As a result, the signal paths need to be individually calibrated.
Furthermore, the large number of data cables 22 (one per transceiver unit 50) and also the number of power cables mean that the connection between the central processing unit and the transceiver unit 50 need to be strictly quality controlled to avoid the wrong one of the transceiver unit 50 being connected to the central processing unit 20.
The large number of data cables 22 and the power supply lines 13 add to the weight of the active antenna system 10, as well as increase in the manufacturing complexity.